Field of the Invention
The present invention relates to a technology of inspecting a semiconductor device, a photo device, or a light emitting device.
Description of the Background Art
Nowadays, a technical development that visualizes dynamic behaviors such as generation, acceleration, and recombination of photocarriers (particularly, electrons), what is called carrier dynamics has been expected in fields of a semiconductor and a photo device, particularly in the field of a solar cell. An observation system used in time regions of femtosecond to picosecond is required in the carrier dynamics.
There is performed research and development on an observation system in which an electromagnetic wave (terahertz wave, 1012Hz) in a terahertz region is used. The electromagnetic wave in the terahertz region has high transmissivity like a radio wave and rectilinear traveling property like light, and practical use of the electromagnetic wave is developed in the fields of communication, security, and non-destructive inspection.
For example, in Japanese Patent Application Laid-Open No. 2013-19861, the photo device as an inspection object is irradiated with the light to detect the emitted electromagnetic wave in the terahertz region. The photocarriers (free electrons or holes) excited by the irradiation of the inspection object with the light is accelerated and moved by an internal electric field. Therefore, the electromagnetic wave is emitted to the outside. Characteristics of the photo device are inspected by detecting the emitted electromagnetic wave.
Japanese Patent Application Laid-Open No. 2013-19861 also discloses that a reverse bias voltage is applied to the photo device in order to enhance an S/N ratio of an intensity of the detected electromagnetic wave. The acceleration of the photocarrier is increased by applying the reverse bias voltage, thereby increasing the intensity of the emitted electromagnetic wave.
As to an alternative method for applying an external electric field, Japanese Patent Application Laid-Open No. 2013-72843 proposes that the inspection object is irradiated with the high-intensity electromagnetic wave to apply the reverse bias voltage to a measurement place.
However, in the conventional technology, it is necessary to provide a circuit or light source applying the reverse bias voltage in order to improve the S/N ratio of the electromagnetic wave intensity, which results in an increase of apparatus cost and a troublesome work to optimize a condition.